Light-emitting module, light-emitting panel, and lighting device

ABSTRACT

An object is to provide a light-emitting module in which a light-emitting element suffering a short-circuit failure does not cause wasteful electric power consumption. Another object is to provide a light-emitting panel in which a light-emitting element suffering a short-circuit failure does not allow the reliability of an adjacent light-emitting element to lower. Focusing on heat generated by a light-emitting element suffering a short-circuit failure, provided is a structure in which electric power is supplied to a light-emitting element through a positive temperature coefficient thermistor (PTC thermistor) thermally coupled with the light-emitting element.

This application is a continuation of copending U.S. application Ser.No. 13/371,690, filed on Feb. 13, 2012 which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light-emitting module, alight-emitting panel including a plurality of light-emitting modules,and a lighting device using the light-emitting module. In particular,the invention relates to a light-emitting module including alight-emitting element with a planar light-emitting region, alight-emitting panel including a plurality of the light-emittingmodules, and a lighting device using the light-emitting module.

2. Description of the Related Art

Light-emitting elements, in which a layer that includes a light-emittingorganic compound and spreads as a film (also referred to as EL layer) isprovided between a pair of electrodes, have been known. Suchlight-emitting elements are called organic EL elements, for example, andlight emission can be obtained from the light-emitting organic compoundupon application of a voltage between the pair of electrodes. Inaddition, examples of light-emitting devices using organic EL elementsare display devices, planar lighting devices, and the like. Note that insuch a display device, an organic EL element is formed over an activematrix substrate.

For example, Patent Document 1 discloses a lighting device using anorganic EL element.

REFERENCE

-   Patent Document 1: Japanese Published Patent Application No.    2006-108651

SUMMARY OF THE INVENTION

Incidentally, there has been a problem in that a short-circuit failurecould easily be caused by entry of an extraneous substance between apair of electrodes because the thickness of an EL layer is as thin asseveral tens of nanometers to several hundreds of nanometers. Note thatin this specification, the term “short-circuit failure” is not limitedto the failure in the case where a pair of electrodes short-circuitregardless of voltage application and also includes the failure in thecase where a pair of electrodes short-circuit as a result of voltageapplication (e.g., as a result of current concentration in a portion inwhich an EL layer is locally thin).

A short circuit between the pair of electrodes of an organic EL elementcauses the organic EL element not only to cease lighting but also togenerate heat, which results in wasteful electric power consumption.Further, when another organic EL element is provided to be adjacent tothe short-circuiting organic EL element, the adjacent organic EL elementmight break down or deteriorate due to the heat generated by theshort-circuiting organic EL element.

Further, a short circuit in an organic EL element connected to aconstant-voltage power source in particular might not only ceaselighting of the organic EL element but also cause a fire. This isbecause a great amount of current is supplied from the constant-voltagepower source to the organic EL element whose electric resistance isreduced by the short circuit.

The present invention is made in view of the foregoing technicalbackground. Therefore, an object of one embodiment of the presentinvention is to provide a light-emitting module in which alight-emitting element suffering a short-circuit failure does not causewasteful electric power consumption. Another object of one embodiment ofthe present invention is to provide a light-emitting panel in which alight-emitting element suffering a short-circuit failure does not allowthe reliability of an adjacent light-emitting element to lower.

Another object of one embodiment of the present invention is to providea lighting device in which a light-emitting element suffering ashort-circuit failure does not cause wasteful electric powerconsumption. Another object of one embodiment of the present inventionis to provide a lighting device in which a light-emitting elementsuffering a short-circuit failure does not allow the reliability tolower.

To achieve any of the above objects, the present invention focuses onheat generated by a light-emitting element including a short-circuitfailure. The present invention reaches an idea of a structure in whichelectric power is supplied to a light-emitting element through apositive temperature coefficient thermistor (PTC thermistor) thermallycoupled with the light-emitting element, leading to the solution of theabove problems.

Specifically, one embodiment of the present invention is alight-emitting module including the following: a light-emitting elementincluding a layer that includes a light-emitting organic compoundbetween a pair of electrodes; and a positive temperature coefficientthermistor thermally coupled with the light-emitting element. In thelight-emitting module, electric power is supplied to the light-emittingelement through the positive temperature coefficient thermistor.

The light-emitting module in accordance with any of the aboveembodiments of the present invention has a structure in which electricpower supply to the light-emitting element is through the positivetemperature coefficient thermistor thermally coupled with thelight-emitting element. Because of this structure, heat generated when ashort-circuit failure of the light-emitting element occurs can bedetected by the positive temperature coefficient thermistor, and theelectric power supply to the light-emitting element can be interruptedor inhibited. Thus, it is possible to provide a light-emitting module inwhich a light-emitting element suffering a short-circuit failure doesnot cause wasteful electric power consumption.

Another embodiment of the present invention is a light-emitting moduleincluding the following: a light-emitting element including a layer thatincludes a light-emitting organic compound between a pair of electrodes;and a positive temperature coefficient thermistor thermally coupled withthe light-emitting element. In the light-emitting module, electric poweris supplied to the light-emitting element through the positivetemperature coefficient thermistor, one of the pair of electrodestransmits light emitted by the layer including the light-emittingorganic compound, and the positive temperature coefficient thermistor isprovided on the side of the other of the pair of electrodes to overlapwith the light-emitting element.

The light-emitting module in accordance with any of the aboveembodiments of the present invention has a structure in which electricpower supply to the light-emitting element is through the positivetemperature coefficient thermistor thermally coupled with thelight-emitting element and the light-emitting element includes anelectrode that transmits light emitted by the layer including thelight-emitting organic compound as one of the pair of electrodes, andwhich includes the positive temperature coefficient thermistor on theside of the other of the pair of electrodes. Because of this structure,heat generated when a short-circuit failure of the light-emittingelement occurs can be detected by the positive temperature coefficientthermistor, and the electric power supply to the light-emitting elementcan be interrupted or inhibited. Further, light emission can beextracted through one of the pair of electrodes of the light-emittingelement which can transmit light, that is, the electrode toward whichthe positive temperature coefficient thermistor is not provided. Thus,it is possible to provide a light-emitting module in which alight-emitting element suffering a short-circuit failure does not causewasteful electric power consumption, or a light-emitting module in whichthe positive temperature coefficient thermistor does not intercept lightemitted by the light-emitting element.

Another embodiment of the present invention is a light-emitting modulewhich has any of the above structures and in which the light-emittingelement and the positive temperature coefficient thermistor arethermally coupled through an electrically conductive material.

The light-emitting module in accordance with any of the aboveembodiments of the present invention has a structure in which electricpower supply to the light-emitting element is through the positivetemperature coefficient thermistor thermally coupled with thelight-emitting element through an electrically conductive material.Because of this structure, the electrically conductive material has bothfunctions of supplying electric power to the light-emitting element andof conducting heat generated by the light-emitting element to thepositive temperature coefficient thermistor. Accordingly, withoutenlargement of the external shape of the light-emitting module, heatgenerated when a short-circuit failure of the light-emitting elementoccurs can be detected by the positive temperature coefficientthermistor, and the electric power supply to the light-emitting elementcan be interrupted or inhibited. Thus, it is possible to provide alight-emitting module in which a light-emitting element suffering ashort-circuit failure does not cause wasteful electric powerconsumption.

Another embodiment of the present invention is a light-emitting modulewhich has any of the above structures and in which electric power issupplied through, instead of the positive temperature coefficientthermistor, a positive temperature coefficient thermistor array in whicha plurality of positive temperature coefficient thermistors is connectedin series.

The light-emitting module in accordance with any of the aboveembodiments of the present invention has a structure in which electricpower supply to the light-emitting element is through a positivetemperature coefficient thermistor array which is thermally coupled withthe light-emitting element and in which a plurality of positivetemperature coefficient thermistors is connected in series. Because ofthis structure, while dividing the light-emitting element into aplurality of regions, the plurality of positive temperature coefficientthermistors constituting the positive temperature coefficient thermistorarray can detect heat generated when a short-circuit failure of thelight-emitting element occurs, and the electric power supply to thelight-emitting element can be interrupted or inhibited. Thus, it ispossible to provide a light-emitting module in which, even when theshort-circuit failure of the light-emitting element is small for itsarea, the positive temperature coefficient thermistor array does notmiss the local heat generation and the light-emitting element causing ashort-circuit failure does not cause wasteful electric powerconsumption.

Another embodiment of the present invention is a light-emitting panelincluding a plurality of adjacent light-emitting modules having any ofthe above structures.

The light-emitting panel in accordance with any of the above embodimentsof the present invention has a structure including a plurality ofadjacent light-emitting modules in each of which electric power issupplied to the light-emitting element through the positive temperaturecoefficient thermistor thermally coupled with the light-emittingelement. Because of this structure, heat generated when a short-circuitfailure of the light-emitting element occurs can be detected by thepositive temperature coefficient thermistor, and the electric powersupply to the light-emitting element can be interrupted or inhibited.Thus, it is possible to provide a light-emitting panel in which alight-emitting element suffering a short-circuit failure does not causewasteful electric power consumption, or a light-emitting panel in whicha light-emitting element suffering a short-circuit failure does notallow the reliability of an adjacent light-emitting element to lower.

Another embodiment of the present invention is a lighting device usingany of the above light-emitting modules.

In the lighting device in accordance with any of the above embodimentsof the present invention, a light-emitting module having a structure inwhich electric power supply to the light-emitting element is through thepositive temperature coefficient thermistor thermally coupled with thelight-emitting element is used. Because of this structure, heatgenerated when a short-circuit failure of the light-emitting elementoccurs can be detected by the positive temperature coefficientthermistor, and the electric power supply to the light-emitting elementcan be interrupted or inhibited. Thus, it is possible to provide alighting device in which a light-emitting element suffering ashort-circuit failure does not cause wasteful electric powerconsumption.

Note that in this specification, the term “EL layer” refers to a layerprovided between a pair of electrodes in a light-emitting element.Therefore, a light-emitting layer including an organic compound that isa light-emitting substance, which is interposed between electrodes, isone mode of an EL layer.

In this specification, the state where two components are thermallycoupled refers to the state where two components are located so thatheat can be conducted therebetween. Therefore, the state where twocomponents are thermally coupled is not limited to the state where theyare in direct contact with each other, and can be the state where acomponent serving as a heating medium is interposed between the twocomponents.

In accordance with one embodiment of the present invention, it ispossible to provide any of the following: a light-emitting module inwhich a light-emitting element suffering a short-circuit failure doesnot cause wasteful electric power consumption; a light-emitting panel inwhich a light-emitting element suffering a short-circuit failure doesnot allow the reliability of an adjacent light-emitting element tolower; a lighting device in which a light-emitting element suffering ashort-circuit failure does not cause wasteful electric powerconsumption; and a light-emitting module in which a light-emittingelement causing a short-circuit failure does not allow the reliabilityto lower.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A to 1C each illustrate a light-emitting module in accordancewith one embodiment;

FIGS. 2A and 2B illustrate a light-emitting module in accordance withone embodiment;

FIGS. 3A and 3B illustrate a light-emitting module in accordance withone embodiment;

FIG. 4 illustrates a light-emitting panel in accordance with oneembodiment;

FIGS. 5A to 5C each illustrate a structure of a light-emitting elementin accordance with one embodiment;

FIGS. 6A and 6B each illustrate a structure of a light-emitting elementin accordance with one embodiment;

FIGS. 7A and 7B illustrate lighting devices each using a light-emittingdevice in accordance with one embodiment;

FIGS. 8A and 8B illustrate a light-emitting module in accordance withone embodiment; and

FIG. 9 illustrates a light-emitting module in accordance with oneembodiment.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments will be described in detail with reference to theaccompanying drawings. Note that the present invention is not limited tothe description given below, and it will be easily understood by thoseskilled in the art that various changes and modifications can be madewithout departing from the spirit and scope of the invention. Therefore,the invention should not be construed as being limited to thedescription in the following embodiments. Note also that in thestructures of one embodiment of the present invention described below,the same reference numerals in different drawings represent componentsthat are identical or have similar functions, the description of whichis not repeated.

[Embodiment 1]

With reference to FIGS. 1A to 1C, this embodiment illustrates alight-emitting module having a structure in which electric power issupplied to a light-emitting element through a positive temperaturecoefficient thermistor thermally coupled with the light-emittingelement, and specifically illustrates a light-emitting module includingan organic EL element over a substrate and a positive temperaturecoefficient thermistor thermally coupled with the organic EL element, inwhich electric power is supplied to the organic EL element through thepositive temperature coefficient thermistor.

A structure of a light-emitting module 150 in accordance with oneembodiment of the present invention is illustrated in FIG. 1A. Thelight-emitting module 150 exemplified in FIG. 1A includes alight-emitting element 130 and a positive temperature coefficientthermistor 140 over a substrate 100. In addition, the light-emittingelement 130 is separated from impurities in the air by a sealant 158, asealing material 159, and the substrate 100 which enclose thelight-emitting element 130.

The substrate 100 has a property of transmitting light emitted by thelight-emitting element 130. The light-emitting element 130 includes afirst electrode 101 in contact with the substrate 100, a partition 104covering an end portion of the first electrode 101, a second electrode102 overlapping with the first electrode 101, and a layer 103 includinga light-emitting organic compound between the first electrode 101 andthe second electrode 102. The positive temperature coefficientthermistor 140 includes a PTC layer 143 having a positive temperaturecoefficient between an upper electrode 142 and a lower electrode 141.

The first electrode 101 of the light-emitting element 130 iselectrically connected to a first terminal 151 of the light-emittingmodule 150. The second electrode 102 of the light-emitting element 130is not only electrically connected to the upper electrode 142 of thepositive temperature coefficient thermistor 140, but also conducts heatgenerated by the light-emitting element 130 to the positive temperaturecoefficient thermistor 140. In addition, the lower electrode 141 iselectrically connected to a second terminal 152 of the light-emittingmodule 150.

The light-emitting module 150 described above has, but is not limitedto, a structure in which the light-emitting element 130 and the positivetemperature coefficient thermistor 140 are electrically connected andthermally coupled through the second electrode 102 of the light-emittingelement. For example, the light-emitting element and the positivetemperature coefficient thermistor may be electrically connected andthermally coupled through the first electrode of the light-emittingelement, although such a structure is not shown in the drawing.Alternatively, the light-emitting element and the positive temperaturecoefficient thermistor may be thermally coupled through the secondelectrode of the light-emitting element and electrically connectedthrough the first electrode of the light-emitting element.Alternatively, the light-emitting element and the positive temperaturecoefficient thermistor may be thermally coupled through the firstelectrode of the light-emitting element and electrically connectedthrough the second electrode of the light-emitting element.

(Material Connecting Light-Emitting Element and Positive TemperatureCoefficient Thermistor)

The light-emitting element and the positive temperature coefficientthermistor are electrically connected and thermally coupled. Forexample, in the light-emitting module exemplified in FIG. 1A, thelight-emitting element and the positive temperature coefficientthermistor are electrically connected and thermally coupled by thesecond electrode 102 and the upper electrode 142 which are formed with acontinuous layer. However, a component that electrically connects thelight-emitting element and the positive temperature coefficientthermistor and a component that thermally bonds the light-emittingelement and the positive temperature coefficient thermistor are notnecessarily the same. For example, the following structure is possible:one component electrically connects the light-emitting element and thepositive temperature coefficient thermistor, and another componentthermally bonds the light-emitting element and the positive temperaturecoefficient thermistor.

As the material that electrically connects the light-emitting element130 and the positive temperature coefficient thermistor 140, a materialhaving high electrical conductivity is preferred, and specifically ametal film containing an element selected from Al, Cr, Cu, Ta, Ti, Mo,and W, an alloy film containing any of these elements as a component, ametal nitride film (e.g., a titanium nitride film, a molybdenum nitridefilm, or a tungsten nitride film), or the like can be used. In order toavoid a problem of heat resistance or corrosiveness, the followingstructure is possible: a film of a high-melting point metal such as Ti,Mo, W, Cr, Ta, Nd, Sc, or Y, or a metal nitride film thereof (e.g., atitanium nitride film, a molybdenum nitride film, or a tungsten nitridefilm) is stacked on one or both of the lower and upper sides of a filmof a metal such as Al or Cu.

As the material that thermally bonds the light-emitting element 130 andthe positive temperature coefficient thermistor 140, a material havinghigh thermal conductivity is preferred. The material having high thermalconductivity, typical examples of which are metals, does not necessarilyhave electrical conductance as well. For example, the followingstructure is possible: thermal bonding is formed using grease havingthermal conductance or a material having an insulating property and highthermal conductivity, which is specifically silicone grease or siliconeresin in which filler having high thermal conductivity is dispersed,while electrical connection is formed using a separate material, whichhas electrical conductivity.

As a material having both high electrical conductivity and high thermalconductivity, a metal having both high electrical conductivity and highthermal conductivity can be used alone or used so as to form a stackedstructure with another material. For example, gold (Au), silver (Ag),copper (Cu), or aluminum (Al) is preferred. An example in which aplurality of materials is used to form a stacked structure may be asfollows: an electrically conductive material which has a work functionhaving a value contributing to excellent carrier injection, and highreflectivity is used for the layer in contact with the layer 103including a light-emitting organic compound, and a material having highelectrical conductivity and/or a material having high thermalconductivity, in particular, is/are used to be stacked over theelectrically conductive material.

When the first terminal 151 and the second terminal 152 in thelight-emitting module 150 having the above structure are connected to apower source, electric power can be supplied to the light-emittingelement 130 through the positive temperature coefficient thermistor 140.Further, the layer 103 including a light-emitting organic compound inthe light-emitting element 130 supplied with the electric power emitslight toward and through the first electrode 101. Furthermore, when ashort-circuit failure occurs in the light-emitting element 130,generated heat is conducted to the positive temperature coefficientthermistor 140 connected to the second electrode 102. The heat isdetected by the positive temperature coefficient thermistor 140, so thatthe electric power supply to the light-emitting element can beinterrupted or inhibited.

(Material Which Can Be Used for PTC Layer Having Positive TemperatureCoefficient)

As a material that can be used for the PTC layer 143 having a positivetemperature coefficient, for example, a material in which electricallyconductive filler is dispersed in a high molecular material or amaterial in which a rare earth element is added as an impurity to bariumtitanate can be used.

The material in which electrically conductive filler is dispersed in ahigh molecular material (also referred to as polymer positivetemperature coefficient [PPTC] material) is preferred, because the PPTCmaterial can easily be reduced in size and has low electric resistancein the conduction state. As the high molecular material that can be usedfor the PPTC material, a high molecule having an insulating propertysuch as polyethylene or polyvinylidene fluoride is preferred; as theelectrically conductive filler, carbon black, nickel powder, or the likeis preferred.

As the positive temperature coefficient thermistor, one having anoperating temperature appropriate for the heat resistance of thelight-emitting element can be selected; for example, one which canoperate at temperatures greater than or equal to 100° C. and less thanor equal to 200° C. can be used. This is because many of lightingdevices are used in an environment where the temperature does not exceed100° C. and because use at temperatures exceeding the glass-transitiontemperature of the light-emitting organic compound in the layerincluding the organic compound allows the reliability of thelight-emitting element to lower. When the positive temperaturecoefficient thermistor is used at temperatures exceeding its operatingtemperature, it rapidly increases in electric resistance, andaccordingly, operation of the positive temperature coefficientthermistor leads to interruption or inhibition of electric power supplyto the light-emitting element connected to the positive temperaturecoefficient thermistor. Thus, a light-emitting element causing ashort-circuit failure can be prevented from continuing generating heatat temperatures exceeding the operating temperature of the positivetemperature coefficient thermistor.

The light-emitting module in accordance with any of the aboveembodiments of the present invention has a structure in which electricpower supply to the light-emitting element is through the positivetemperature coefficient thermistor thermally coupled with thelight-emitting element. Because of this structure, heat generated when ashort-circuit failure of the light-emitting element occurs can bedetected by the positive temperature coefficient thermistor, and theelectric power supply to the light-emitting element can be interruptedor inhibited. Thus, it is possible to provide a light-emitting module inwhich a light-emitting element suffering a short-circuit failure doesnot cause wasteful electric power consumption.

The light-emitting module in accordance with the above embodiment of thepresent invention has a structure in which electric power supply to thelight-emitting element is through the positive temperature coefficientthermistor thermally coupled with the light-emitting element through anelectrically conductive material. Because of this structure, theelectrically conductive material has both functions of supplyingelectric power to the light-emitting element and of conducting heatgenerated by the light-emitting element to the positive temperaturecoefficient thermistor. Accordingly, heat generated when theshort-circuit failure of the light-emitting element occurs can bedetected by the positive temperature coefficient thermistor, and theelectric power supply to the light-emitting element can be interruptedor inhibited. Thus, it is possible to provide a light-emitting module inwhich a light-emitting element suffering a short-circuit failure doesnot cause wasteful electric power consumption.

(Modification Example 1)

Another mode of a light-emitting module in accordance with oneembodiment of the present invention is illustrated in FIG. 1B. Thelight-emitting module 150 exemplified in FIG. 1B includes the positivetemperature coefficient thermistor 140 over the substrate 100 and thelight-emitting element 130 over the positive temperature coefficientthermistor 140. In addition, the light-emitting element 130 is separatedfrom impurities in the air by the sealant 158 which surrounds thelight-emitting element 130 and the sealing material 159 which cantransmit light emitted by the light-emitting element 130.

The positive temperature coefficient thermistor 140 is included betweenthe substrate 100 and the light-emitting element 130. The positivetemperature coefficient thermistor 140 includes the PTC layer 143 havinga positive temperature coefficient between the lower electrode 141 andthe first electrode 101 of the light-emitting element.

The positive temperature coefficient thermistor 140 may be provided overthe substrate 100 in such a way that the separately fabricated positivetemperature coefficient thermistor 140 is mounted on a surface of thesubstrate 100, or in such a way that the PTC layer 143 having a positivetemperature coefficient is stacked over the lower electrode 141 providedover a surface of the substrate 100, an end portion of the firstelectrode 101 is covered with the partition 104 having an insulatingproperty, and the first electrode 101 of the light-emitting element 130which also serves as the upper electrode is stacked over the PTC layer143. The PTC layer 143 having a positive temperature coefficient may beformed over the lower electrode 141 in such a way that, for example, aPTC material processed into a sheet is laminated or transferred.

The light-emitting element 130 includes the first electrode 101 formedover the PTC layer 143, the partition 104 covering an end portion of thefirst electrode 101, and the layer 103 including a light-emittingorganic compound between the first electrode and the second electrode102 overlapping with the first electrode.

In this modification example, one of the electrodes of the positivetemperature coefficient thermistor 140 also serves as the firstelectrode 101 of the light-emitting element 130, so that thelight-emitting element 130 and the positive temperature coefficientthermistor 140 are electrically connected and thermally coupled witheach other. Therefore, in a preferred structure, the first electrode 101includes an electrically conductive material having high thermalconductivity; in a particularly preferred structure, a metal having highelectrical conductivity and high thermal conductivity is used alone orused so as to form a stacked structure with another electricallyconductive material. Note that an electrically conductive materialhaving a property of transmitting light emitted by the layer 103including a light-emitting organic compound is used for the secondelectrode 102 of the light-emitting element 130.

When the first terminal 151 and the second terminal 152 in thelight-emitting module 150 having the above structure are connected to apower source, electric power can be supplied to the light-emittingelement 130 through the positive temperature coefficient thermistor 140.Further, the layer 103 including a light-emitting organic compound inthe light-emitting element 130 supplied with the electric power emitslight toward and through the second electrode 102. Furthermore, when ashort-circuit failure occurs in the light-emitting element 130,generated heat is conducted to the positive temperature coefficientthermistor 140 provided in contact with the first electrode 101. Theheat is detected by the positive temperature coefficient thermistor 140,so that the electric power supply to the light-emitting element can beinterrupted or inhibited.

The light-emitting module in accordance with any of the aboveembodiments of the present invention has a structure in which electricpower supply to the light-emitting element is through the positivetemperature coefficient thermistor thermally coupled with thelight-emitting element and the light-emitting element includes anelectrode that transmits light emitted by the layer including thelight-emitting organic compound as one of the pair of electrodes, andwhich includes the positive temperature coefficient thermistor on theside of the other of the pair of electrodes. Because of this structure,heat generated when a short-circuit failure of the light-emittingelement occurs can be detected by the positive temperature coefficientthermistor, and the electric power supply to the light-emitting elementcan be interrupted or inhibited. Further, light emission can beextracted through one of the pair of electrodes of the light-emittingelement which can transmit light, that is, the electrode toward whichthe positive temperature coefficient thermistor is not provided. Thus,it is possible to provide a light-emitting module in which alight-emitting element suffering a short-circuit failure does not causewasteful electric power consumption, or a light-emitting module in whichthe positive temperature coefficient thermistor does not intercept lightemitted by the light-emitting element.

(Modification Example 2)

Another mode of a light-emitting module in accordance with oneembodiment of the present invention is illustrated in FIG. 1C. In thelight-emitting module 150 exemplified in FIG. 1C, the light-emittingelement 130 on one side of the substrate 100 and the positivetemperature coefficient thermistor 140 on the opposite side of thesubstrate 100 are included so as to overlap with each other. Inaddition, the light-emitting element 130 is separated from impurities inthe air by the sealant 158 which surrounds the light-emitting element130 and the sealing material 159 which can transmit light emitted by thelight-emitting element 130.

The sides of the substrate 100 each have an insulating surface, one ofwhich is provided with the first electrode 101 of the light-emittingelement 130 and the opposite of which is provided with the lowerelectrode 141 of the positive temperature coefficient thermistor 140.The light-emitting element 130 includes the first electrode 101 incontact with the one side of the substrate 100, the partition 104covering an end portion of the first electrode 101, the second electrode102 overlapping with the first electrode 101, and the layer 103including a light-emitting organic compound between the first electrode101 and the second electrode 102. The positive temperature coefficientthermistor 140 includes the PTC layer 143 having a positive temperaturecoefficient between the lower electrode 141 in contact with the oppositesurface of the substrate 100 and the upper electrode 142.

The first electrode 101 of the light-emitting element 130 iselectrically connected to the lower electrode 141 of the positivetemperature coefficient thermistor 140 through an opening providedthrough the substrate 100. In addition, the lower electrode 141 of thepositive temperature coefficient thermistor 140 conducts heat generatedby the light-emitting element 130 to the positive temperaturecoefficient thermistor 140 through the opening provided through thesubstrate 100. The upper electrode 142 of the positive temperaturecoefficient thermistor 140 is electrically connected to the firstterminal 151 of the light-emitting module 150. In addition, the secondelectrode 102 of the light-emitting element 130 is electricallyconnected to the second terminal 152 of the light-emitting module 150.

In this modification example, the lower electrode 141 of the positivetemperature coefficient thermistor 140 and the first electrode 101 ofthe light-emitting element 130 are connected through the opening throughthe substrate, so that the light-emitting element 130 and the positivetemperature coefficient thermistor 140 are electrically connected andthermally coupled. Therefore, in a preferred structure, the lowerelectrode 141 includes an electrically conductive material having highthermal conductivity; in a particularly preferred structure, a metalhaving high electrical conductivity and high thermal conductivity isused alone or used so as to form a stacked structure with anotherelectrically conductive material. Note that an electrically conductivematerial having a property of transmitting light emitted by the layer103 including a light-emitting organic compound is used for the secondelectrode 102 of the light-emitting element 130.

When the first terminal 151 and the second terminal 152 in thelight-emitting module 150 having the above structure are connected to apower source, electric power can be supplied to the light-emittingelement 130 through the positive temperature coefficient thermistor 140.Further, the layer 103 including a light-emitting organic compound inthe light-emitting element 130 supplied with the electric power emitslight toward and through the second electrode 102. Furthermore, when ashort-circuit failure occurs in the light-emitting element 130,generated heat is conducted to the positive temperature coefficientthermistor 140 connected to the first electrode 101. The heat isdetected by the positive temperature coefficient thermistor 140, so thatthe electric power supply to the light-emitting element can beinterrupted or inhibited.

The light-emitting module in accordance with any of the aboveembodiments of the present invention has a structure in which electricpower supply to the light-emitting element is through the positivetemperature coefficient thermistor thermally coupled with thelight-emitting element and the light-emitting element includes anelectrode that transmits light emitted by the layer including thelight-emitting organic compound as one of the pair of electrodes, andwhich includes the positive temperature coefficient thermistor on theside of the other of the pair of electrodes. Because of this structure,heat generated when a short-circuit failure of the light-emittingelement occurs can be detected by the positive temperature coefficientthermistor, and the electric power supply to the light-emitting elementcan be interrupted or inhibited. Further, light emission can beextracted through one of the pair of electrodes of the light-emittingelement which can transmit light, that is, the electrode toward whichthe positive temperature coefficient thermistor is not provided. Thus,it is possible to provide a light-emitting module in which alight-emitting element suffering a short-circuit failure does not causewasteful electric power consumption, or a light-emitting module in whichthe positive temperature coefficient thermistor does not intercept lightemitted by the light-emitting element.

This embodiment can be combined as appropriate with any of the otherembodiments described in this specification.

[Embodiment 2]

With reference to FIGS. 2A and 2B, this embodiment illustrates alight-emitting module having a structure where electric power issupplied to a light-emitting element through a positive temperaturecoefficient thermistor array in which a plurality of positivetemperature coefficient thermistors is connected in series and which isthermally coupled with the light-emitting element, and specificallyillustrates a light-emitting module including an organic EL element overa substrate and a positive temperature coefficient thermistor array inwhich a plurality of positive temperature coefficient thermistors isconnected in series and which is thermally coupled with the organic ELelement, where electric power is supplied to the organic EL elementthrough the positive temperature coefficient thermistor array.

A top view of a structure of a light-emitting module 250 in accordancewith one embodiment of the present invention is illustrated in FIG. 2A,and a cross section taken along the section lines A-A′ and B-B′ of FIG.2A is illustrated in FIG. 2B.

The light-emitting module 250 exemplified in FIGS. 2A and 2B includes,over a substrate 200, a light-emitting element 230 and nine positivetemperature coefficient thermistors including a positive temperaturecoefficient thermistor 240 a, a positive temperature coefficientthermistor 240 b, and a positive temperature coefficient thermistor 240c. Further, FIG. 2B illustrates a sealant 258 which surrounds thelight-emitting element 230 and a sealing material 259 which can transmitlight emitted by the light-emitting element 230. The light-emittingelement 230 is separated from impurities in the air by the sealant 258and the sealing material 259.

For the substrate 200, a material having high thermal conductivity ispreferred. This is because the substrate functions as a heat sink whichexhausts heat generated by the light-emitting element 230 that operateswithout causing abnormal heat generation. As a substrate that has aninsulating surface on the side where the element is mounted and has highthermal conductivity as a whole, a metal substrate with a surfacecovered with a material having an insulating property, and the like canbe an example.

A structure of the positive temperature coefficient thermistor arrayincluded in the light-emitting module 250 is described with reference toFIGS. 3A and 3B. A top view of the positive temperature coefficientthermistor array 240 is illustrated in FIG. 3A. The positive temperaturecoefficient thermistor array 240 includes the nine positive temperaturecoefficient thermistors (240 a, 240 b, 240 c, 240 d, 240 e, 240 f, 240g, 240 h, and 240 i) connected in series.

An example of the way how the positive temperature coefficientthermistors are connected in series is described with reference to FIG.3B. FIG. 3B is a cross-sectional view of the positive temperaturecoefficient thermistors 240 a, 240 b, and 240 c, and the positivetemperature coefficient thermistors are connected to each other inseries. Note that the positive temperature coefficient thermistor 240 aincludes a PTC layer 243 a between a lower electrode 241 a in contactwith the substrate 200 and an upper electrode 242 a; the positivetemperature coefficient thermistor 240 b includes a PTC layer 243 b abetween a lower electrode 241 b in contact with the substrate 200 and anupper electrode 242 b; and the positive temperature coefficientthermistor 240 c includes a PTC layer 243 c between a lower electrode241 c in contact with the substrate 200 and an upper electrode 242 c.

The upper electrodes 242 a and 242 b in the positive temperaturecoefficient thermistors 240 a and 240 b are connected to each other, andthe lower electrodes 241 b and 241 c in the positive temperaturecoefficient thermistors 240 b and 240 c are connected to each other. Insuch a structure, the positive temperature coefficient thermistors areconnected to each other in series, so that current flows through thepositive temperature coefficient thermistors 240 a, 240 b, and 240 c asindicated by the thick arrow illustrated in FIG. 3B. Note that in FIG.3A, the thick arrow represents an example of current flowing through thepositive temperature coefficient thermistor array 240.

The positive temperature coefficient thermistor array 240 having such astructure is thermally coupled with the light-emitting element 230;thus, while the light-emitting element 230 is divided into a pluralityof regions (nine regions in this embodiment), heat generated when ashort-circuit failure of the light-emitting element 230 occurs can bemonitored. Then, the heat generated when a short-circuit failure occursin one of the plurality of regions is detected, and accordingly, theelectric power supply to the light-emitting element can be interruptedor inhibited. Thus, it is possible to provide a light-emitting module inwhich, even when the short-circuit failure of the light-emitting elementis small for its area, the positive temperature coefficient thermistorarray does not miss the local heat generation and thus thelight-emitting element causing a short-circuit failure does not causewasteful electric power consumption.

The light-emitting element 230 included in the light-emitting module 250includes a first electrode 201 over a planarization film 247 providedover the positive temperature coefficient thermistor array, a partition204 covering an end portion of the first electrode 201, a secondelectrode 202 overlapping with the first electrode 201, and a layer 203including a light-emitting organic compound between the first electrode201 and the second electrode 202 (see FIG. 2B).

For the second electrode 202 of the light-emitting element 230, anelectrically conductive material having a property of transmitting lightemitted by the layer 203 including a light-emitting organic compound isused. Further, an end portion of the second electrode 202 is connectedto a second terminal 252 of the light-emitting module 250.

The first electrode 201 of the light-emitting element 230 iselectrically connected to the upper electrode 242 c of the positivetemperature coefficient thermistor array 240 through an opening providedthrough the planarization film 247. Further, the light-emitting element230 and the positive temperature coefficient thermistor array 240 arethermally coupled through the planarization film 247.

The planarization film 247 is used in order to planarize a surface ofthe first electrode 201 used in the light-emitting element 230. For theplanarization film 247, a resin material such as polyimide, acrylic,benzocyclobutene, polyamide, or epoxy can be used. Other than such aresin material, a low dielectric constant material (low-k material), asiloxane-based resin, phosphosilicate glass (PSG), borophosphosilicateglass (BPSG), or the like can be used. In particular, a material havinghigh thermal conductivity is preferably included. In this embodiment, amaterial having an insulating property is preferred, because the upperelectrodes of the positive temperature coefficient thermistorsconstituting the positive temperature coefficient thermistor array needto be insulated from the first electrode of the light-emitting element.Further, a film having a high barrier property may be stacked in orderto prevent diffusion of impurities into the light-emitting element.

The lower electrode of the positive temperature coefficient thermistoris connected to the first terminal 251 of the light-emitting module 250through an opening provided through the planarization film 247.

When the first terminal 251 and the second terminal 252 in thelight-emitting module 250 having the above structure are connected to apower source, electric power can be supplied to the light-emittingelement 230 through the positive temperature coefficient thermistorarray 240. Further, the layer 203 including a light-emitting organiccompound in the light-emitting element 230 supplied with the electricpower emits light toward and through the second electrode 202.Furthermore, when a short-circuit failure occurs in the light-emittingelement 230, generated heat is conducted through the planarization film247 to any of the plurality of positive temperature coefficientthermistors provided in the positive temperature coefficient thermistorarray 240. Since the positive temperature coefficient thermistorsconstituting the positive temperature coefficient thermistor array 240are connected in series, detection of the heat due to the short-circuitfailure by at least one of the positive temperature coefficientthermistors enables the positive temperature coefficient thermistorarray to interrupt or inhibit electric power supply to thelight-emitting element. In other words, generation of a short-circuitfailure in the light-emitting element 230 can be monitored in each ofthe regions into which division is made by the plurality of positivetemperature coefficient thermistors.

The light-emitting module in accordance with any of the aboveembodiments of the present invention has a structure in which electricpower supply to the light-emitting element is through a positivetemperature coefficient thermistor array which is thermally coupled withthe light-emitting element and in which a plurality of positivetemperature coefficient thermistors is connected in series. Because ofthis structure, while dividing the light-emitting element into aplurality of regions, the plurality of positive temperature coefficientthermistors constituting the positive temperature coefficient thermistorarray can detect heat generated when a short-circuit failure of thelight-emitting element occurs, and the electric power supply to thelight-emitting element can be interrupted or inhibited. Thus, it ispossible to provide a light-emitting module in which, even when theshort-circuit failure of the light-emitting element is small for itsarea, the positive temperature coefficient thermistor array does notmiss the local heat generation and the light-emitting element causing ashort-circuit failure does not cause wasteful electric powerconsumption.

This embodiment can be combined as appropriate with any of the otherembodiments described in this specification.

[Embodiment 3]

With reference to FIGS. 8A and 8B, this embodiment illustrates alight-emitting module having a plurality of structures provided inparallel in each of which electric power is supplied to a light-emittingelement through a positive temperature coefficient thermistor thermallycoupled with the light-emitting element, and specifically illustrates astructure in which a plurality of organic EL elements is provided in amatrix over upper electrodes of the positive temperature coefficientthermistors provided over a substrate. Note that each positivetemperature coefficient thermistor and one of the organic EL elementsare thermally coupled and electrically connected in series.

A top view of a structure of a light-emitting module 450 in accordancewith one embodiment of the present invention is illustrated in FIG. 8A,and a cross section taken along the section lines A-A′ and B-B′ of FIG.8A is illustrated in FIG. 8B.

The light-emitting module 450 illustrated as an example in FIG. 8Aincludes a light-emitting element matrix 430. Note that seven rows andseven columns of light-emitting elements are provided in the exemplifiedlight-emitting element matrix 430. As illustrated in FIG. 8B, thelight-emitting module 450 includes positive temperature coefficientthermistors 440 between the light-emitting element matrix 430 and asubstrate 400.

Each positive temperature coefficient thermistor 440 includes a lowerelectrode 441, a PTC layer 443 having a positive temperature coefficientover the lower electrode 441, and an upper electrode over the PTC layer443. For simplification of manufacture, the lower electrodes 441 of thepositive temperature coefficient thermistors 440 may be formed as asingle continuous layer and the PTC layers 443 of the positivetemperature coefficient thermistors 440 may also be formed as a singlecontinuous layer, as illustrated in the drawing. The upper electrodes ofthe positive temperature coefficient thermistors 440 exemplified in thisembodiment, which have been divided into seven rows and seven columns,also serve as first electrodes of the light-emitting elementsconstituting the light-emitting element matrix 430.

The light-emitting elements constituting the light-emitting elementmatrix 430 are formed over the positive temperature coefficientthermistor 440. The light-emitting elements exemplified in thisembodiment each include the first electrode serving as the upperelectrode of the positive temperature coefficient thermistor 440, apartition 404 covering an end portion of the first electrode, a layer403 including a light-emitting organic compound which is in contact withthe first electrode in an opening of the partition 404, and a secondelectrode 402 in contact with the layer 403 including a light-emittingorganic compound. For example, a first electrode 401 illustrated in FIG.8B is one of the upper electrodes of the positive temperaturecoefficient thermistors 440 and is one of the first electrodes arrangedin seven rows and seven columns In addition, the first electrode 401 andthe layer 403 including a light-emitting organic compound are in contactwith each other in the opening of the partition 404.

Further, FIG. 8B illustrates a sealant 458 which surrounds thelight-emitting element matrix 430 and a sealing material 459 which cantransmit light emitted by the light-emitting element matrix 430. Thelight-emitting element matrix 430 is separated from impurities in theair by the sealant 458 and the sealing material 459.

The light-emitting element matrix 430 and the positive temperaturecoefficient thermistors 440 which constitute the light-emitting module450 can be fabricated using the same materials as those of thelight-emitting element and the positive temperature coefficientthermistor described in Embodiment 2.

The light-emitting module 450 having such a structure includes a matrixwith seven rows and seven columns of units in each of which the positivetemperature coefficient thermistor 440 and the light-emitting elementare electrically connected in series, and the units are electricallyconnected in parallel through the lower electrodes of the positivetemperature coefficient thermistors 440 (the lower electrodesillustrated in the drawing are formed as a single continuous layer).With such a structure, the PTC layer at temperatures exceeding theoperating temperature of the positive temperature coefficient thermistor440 is more electrically-resistant or -insulated, and accordingly, thePTC layer at temperatures exceeding the operating temperature loseselectrical continuity with another PTC layer to become electricallyisolated.

The light-emitting elements arranged in a matrix of seven rows and sevencolumns are thermally coupled with the PTC layers of the positivetemperature coefficient thermistors 440 with which the first electrodesof the elements are in contact. Therefore, a light-emitting elementsuffering a short-circuit failure heats the PTC layer that is just underthe light-emitting element and that overlaps therewith. The PTC layer attemperatures exceeding the operating temperature of the positivetemperature coefficient thermistor 440 due to heating is moreelectrically-resistant or -insulated, and accordingly, electric powersupply to the first electrode of the light-emitting element connected tothe PTC layer can be interrupted or inhibited.

Note that each light-emitting element in a matrix exemplified in thisembodiment can be formed to have any of a variety of sizes, preferablyhas a size to be difficult to see visibly, which is specifically a sizewith a diameter of 5 mm or less, preferably a minute size with adiameter of 1 mm or less. Without limitation to matrix arrangement, thelight-emitting elements may be irregularly arranged. Further, thelight-emitting elements may have a variety of forms without limitationto a quadrangle, for example, the form in which formless shapes arecontinuous, and specifically may be determined by the shape of theelectrically conductive filler (e.g., carbon black or nickel powder)included in the PTC layer.

(Modification Example)

Another mode of a light-emitting module in accordance with oneembodiment of the present invention is illustrated in FIG. 9. Alight-emitting module 550 exemplified in FIG. 9 includes alight-emitting element 530 and a positive temperature coefficientthermistor 540 over a substrate 500.

The positive temperature coefficient thermistor 540 of this modificationexample exemplified in this embodiment includes a lower electrode 541, aPTC layer 543 having a positive temperature coefficient over the lowerelectrode 541, and an upper electrode over the PTC layer 543. The upperelectrode of the positive temperature coefficient thermistor 540exemplified in this embodiment also serves as a first electrode 501 ofthe light-emitting element 530.

For the first electrode 501 of this embodiment, a material having lowerelectrical conductivity than metals is used. Examples of a material thatcan be used for the first electrode 501 include a film of anelectrically conductive polymer (e.g., a high molecular compound towhich acid is added, such aspoly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic acid) (PEDOT/PSS)and polyaniline/poly(styrenesulfonic acid) (PAni/PSS)), a film in whicha material having an acceptor property (e.g., molybdenum oxide) is mixedinto an organic compound, and a film in which a material having a donorproperty (e.g., Li, alkali metals, or alkaline earth metals) is mixedinto an organic compound.

The first electrode 501 planarizes a surface of the PTC layer 543.Especially the first electrode 501 that can be obtained by filmformation using a coating method is preferred.

The importance of use of a film having reduced electrical conductivityfor the first electrode 501 of the light-emitting element 530, whichalso serves as the upper electrode of the positive temperaturecoefficient thermistor 540, is described below. The light-emittingelement is thermally coupled with the PTC layer of the positivetemperature coefficient thermistor 540 with which the first electrode isin contact. Therefore, when a short-circuit failure occurs in part ofthe light-emitting element, generated heat is conducted to a region inthe PTC layer which overlaps with the short-circuit failure. The regionin the PTC layer at temperatures exceeding the operating temperature ofthe positive temperature coefficient thermistor 540 due to heating ismore electrically-resistant or -insulated, and accordingly, electricpower supply to the first electrode of the light-emitting elementconnected to the region can be interrupted or inhibited.

In such a case, when the electrical conductivity of the first electrode501 of the light-emitting element 530, which also serves as the upperelectrode of the positive temperature coefficient thermistor 540, isreduced, there is an effect of reducing current flowing into theshort-circuit failure portion from the vicinity of the region in the PTClayer at temperatures exceeding the operating temperature of thepositive temperature coefficient thermistor 540.

The light-emitting module 550 having such a structure enables the lightemission area to be enlarged.

The light-emitting module in accordance with the above embodiment of thepresent invention has a plurality of units provided in parallel in eachof which electric power is supplied to the light-emitting elementthrough the positive temperature coefficient thermistor thermallycoupled with the light-emitting element. Because of this structure, heatgenerated when a short-circuit failure of the light-emitting elementoccurs can be detected by a region of the positive temperaturecoefficient thermistor which is thermally coupled with thelight-emitting element, and the electric power supply to thelight-emitting element can be interrupted or inhibited. Thus, it ispossible to provide a light-emitting module in which, even when theshort-circuit failure of the light-emitting module is small for itslight emission area, the positive temperature coefficient thermistordoes not miss the local heat generation and the light-emitting elementcausing a short-circuit failure does not cause wasteful electric powerconsumption.

This embodiment can be combined as appropriate with any of the otherembodiments described in this specification.

[Embodiment 4]

With reference to FIG. 4, this embodiment illustrates a light-emittingpanel including a plurality of adjacent light-emitting modules in whichelectric power is supplied to light-emitting elements through a positivetemperature coefficient thermistor thermally coupled with thelight-emitting elements, and specifically illustrates a light-emittingpanel provided with adjacent light-emitting modules including organic ELelements over a substrate and a positive temperature coefficientthermistor array in which a plurality of positive temperaturecoefficient thermistors is connected in series and which is thermallycoupled with the organic EL elements, where electric power is suppliedto the organic EL elements is through the positive temperaturecoefficient thermistor array.

A top view of a structure of a light-emitting panel 350 in accordancewith one embodiment of the present invention is illustrated in FIG. 4.

The light-emitting panel 350 exemplified in FIG. 4 includes alight-emitting module 250 a, a light-emitting module 250 b, alight-emitting module 250 c, and a light-emitting module 250 d, whichare provided adjacent to each other and have the same structure as thatof the light-emitting module 250 described above in Embodiment 2.

A second terminal 252 a of the light-emitting module 250 a and a firstterminal 251 b of the light-emitting module 250 b are connected to eachother, so that the light-emitting module 250 a and the light-emittingmodule 250 b are connected in series. Further, a second terminal 252 cof the light-emitting module 250 c and a first terminal 251 d of thelight-emitting module 250 d are connected to each other, so that thelight-emitting module 250 c and the light-emitting module 250 d areconnected in series.

A first terminal 251 a and a second terminal 252 b, which are terminalsof the light-emitting modules included in the light-emitting panel 350,are connected to a first constant current power source not shown in thedrawing, while a first terminal 251 c and a second terminal 252 d, whichare also terminals of the light-emitting modules included in thelight-emitting panel 350, are connected to a second constant currentpower source not shown in the drawing. Thus, the light-emitting panel350 can perform lighting with uniform brightness.

Further, when a short-circuit failure occurs in a light-emitting elementof the light-emitting module included in the light-emitting panel 350,generated heat is detected by the positive temperature coefficientthermistor included in the light-emitting module, so that the electricpower supply to the light-emitting element can be interrupted orinhibited. Thus, it is possible to provide a light-emitting panel inwhich a light-emitting element suffering a short-circuit failure doesnot cause wasteful electric power consumption, or a light-emitting panelin which a light-emitting element suffering a short-circuit failure doesnot allow the reliability of an adjacent light-emitting element tolower.

This embodiment can be combined as appropriate with any of the otherembodiments described in this specification.

[Embodiment 5]

This embodiment illustrates an example of a light-emitting element thatcan be used for the light-emitting module having a structure whereelectric power is supplied to a light-emitting element through apositive temperature coefficient thermistor thermally coupled with thelight-emitting element, with reference to FIGS. 5A to 5C and FIGS. 6Aand 6B.

The light-emitting element exemplified in this embodiment includes afirst electrode, a second electrode, and a layer that includes alight-emitting organic compound (hereinafter referred to as an EL layer)between the first electrode and the second electrode. In thisembodiment, the first electrode formed over a substrate functions as ananode, and the second electrode functions as a cathode. The EL layer isprovided between the first electrode and the second electrode, and astructure of the EL layer can be selected as appropriate in accordancewith material properties of the first electrode and second electrode. Anexample of the structure of the light-emitting element is describedbelow; it is needless to say that the structure of the light-emittingelement is not limited to this example.

(Example 1 of Light-Emitting Element Structure)

An example of the structure of the light-emitting element is illustratedin FIG. 5A. In the light-emitting element illustrated in FIG. 5A, an ELlayer 1103 is interposed between an anode 1101 and a cathode 1102.

When a voltage higher than the threshold voltage of the light-emittingelement is applied between the anode 1101 and the cathode 1102, holesfrom the anode 1101 side and electrons from the cathode 1102 side areinjected into the EL layer 1103. The injected electrons and holesrecombine in the EL layer 1103, so that a light-emitting substanceincluded in the EL layer 1103 emits light.

The EL layer 1103 includes at least a light-emitting layer including thelight-emitting substance, and may have a structure in which thelight-emitting layer and a layer other than the light-emitting layer arestacked. Examples of the layer other than the light-emitting layerinclude a layer that includes a substance having a high hole-injectionproperty, a substance having a high hole-transport property, a substancehaving a poor hole-transport property (a substance that blocks holes), asubstance having a high electron-transport property, a substance havinga high electron-injection property, a substance having a bipolarproperty (a substance having a high electron-transport property and ahigh hole-transport property), or the like.

A specific example of a structure of the EL layer 1103 is illustrated inFIG. 5B. In the EL layer 1103 illustrated in FIG. 5B, a hole-injectionlayer 1113, a hole-transport layer 1114, a light-emitting layer 1115, anelectron-transport layer 1116, and an electron-injection layer 1117 arestacked in this order from the anode 1101 side.

(Example 2 of Light-Emitting Element Structure)

Another example of the structure of the light-emitting element isillustrated in FIG. 5C. In the light-emitting element exemplified inFIG. 5C, the EL layer 1103 is interposed between the anode 1101 and thecathode 1102. Further, an intermediate layer 1104 is provided betweenthe cathode 1102 and the EL layer 1103. For the EL layer 1103 in Example2 of Light-Emitting Element Structure, the same structure as that inExample 1 of Light-Emitting Element Structure described above can beapplied, and for the details, the explanation in Example 1 ofLight-Emitting Element Structure can be referred to.

The intermediate layer 1104 is formed to include at least a chargegeneration region, and may have a structure in which the chargegeneration region and a layer other than the charge generation regionare stacked. For example, a structure can be employed in which a firstcharge generation region 1104 c, an electron-relay layer 1104 b, and anelectron-injection buffer 1104 a are stacked in this order from thecathode 1102 side.

The behaviors of electrons and holes in the intermediate layer 1104 aredescribed. When a voltage higher than the threshold voltage of thelight-emitting element is applied between the anode 1101 and the cathode1102, holes and electrons are generated in the first charge generationregion 1104 c, and the holes move into the cathode 1102 and theelectrons move into the electron-relay layer 1104 b. The electron-relaylayer 1104 b, which has a high electron-transport property, rapidlyaccepts the electrons generated in the first charge generation region1104 c and donates them to the electron-injection buffer 1104 a. Theelectron-injection buffer 1104 a can reduce a barrier to electroninjection into the EL layer 1103, so that the efficiency of the electroninjection into the EL layer 1103 can be increased. Thus, the electronsgenerated in the first charge generation region 1104 c are injected intothe LUMO level of the EL layer 1103 through the electron-relay layer1104 b and the electron-injection buffer 1104 a.

In addition, the electron-relay layer 1104 b can prevent interaction inwhich, for example, a substance included in the first charge generationregion 1104 c and a substance included in the electron-injection buffer1104 a react with each other at an interface between the chargegeneration region 1104 c and the electron-injection buffer 1104 a toimpair the functions of the first charge generation region 1104 c andthe electron-injection buffer 1104 a.

(Example 3 of Light-Emitting Element Structure)

Another example of the structure of the light-emitting element isillustrated in FIG. 6A. In the light-emitting element exemplified inFIG. 6A, two EL layers are provided between the anode 1101 and thecathode 1102. Further, the intermediate layer 1104 is provided betweenan EL layer 1103 a and an EL layer 1103 b.

The number of the EL layers provided between the anode and the cathodeis not limited to two. The light-emitting element exemplified in FIG. 6Bhas a structure in which a plurality of EL layers 1103 is stacked, thatis, a stacked-layer element structure. Note that in the case where n ELlayers 1103 are provided between the anode and the cathode (n is anatural number greater than or equal to 2), each intermediate layer 1104is provided between an mth EL layer and an (m+1)th EL layer (m is anatural number greater than or equal to 1 and less than or equal to(n−1)).

For the EL layer 1103 in Example 3 of Light-Emitting Element Structure,the same structure as that in Example 1 of Light-Emitting ElementStructure described above can be applied. As for the intermediate layer1104 in Example 3 of Light-Emitting Element Structure, the samestructure as that in Example 2 of Light-Emitting Element Structuredescribed above can be applied. Therefore, the explanation in Example 1or 2 of Light-Emitting Element Structure can be referred to for thedetails.

The behaviors of electrons and holes in the intermediate layer 1104provided between the EL layers are described. When a voltage higher thanthe threshold voltage of the light-emitting element is applied betweenthe anode 1101 and the cathode 1102, holes and electrons are generatedin the intermediate layer 1104, and the holes move into the EL layerprovided on the cathode 1102 side and the electrons move into the ELlayer provided on the anode 1101 side. The holes injected into the ELlayer provided on the cathode side recombine with the electrons injectedfrom the cathode side, so that the light-emitting substance included inthe EL layer emits light. Further, the electrons injected into the ELlayer provided on the anode side recombine with the holes injected fromthe anode side, so that the light-emitting substance included in the ELlayer emits light. Thus, the holes and electrons generated in theintermediate layer 1104 cause light emission in the different EL layers.

Note that the EL layers can be provided in contact with each other whenthese EL layers allow the same structure as the intermediate layer to beformed therebetween. The EL layers can be provided in contact with eachother specifically when one of the contacting surfaces of the EL layersis provided with a charge generation region, because the chargegeneration region functions as a first charge generation region of theintermediate layer.

Examples 1 to 3 of Light-Emitting Element Structure can be implementedin combination. For example, an intermediate layer can also be providedbetween the cathode and the EL layer in Example 3 of Light-EmittingElement Structure.

[Embodiment 6]

In this embodiment, examples of a lighting device including alight-emitting module in accordance with one embodiment of the presentinvention are described with reference to FIGS. 7A and 7B.

In accordance with one embodiment of the present invention, a lightingdevice in which a light-emitting portion has a curved surface can alsobe realized.

One embodiment of the present invention can also be applied to alighting device for motor vehicles; for example, a lighting device canalso be easily mounted on a dashboard, a ceiling, or the like.

In FIG. 7A, a lighting device 901 provided on the ceiling in a room, alighting device 904 provided on a wall, and a desk lamp 903, to whichone embodiment of the present invention is applied, are illustrated.Since the light-emitting module in accordance with one embodiment of thepresent invention can have a larger area, it can be used for a lightingdevice having a large area.

In FIG. 7B, an example of another lighting device is illustrated. Atable lamp illustrated in FIG. 7B includes a lighting portion 9501, asupport 9503, a support base 9505, and the like. The lighting portion9501 includes the light-emitting module in accordance with oneembodiment of the present invention. In one embodiment of the presentinvention, a lighting device having a curved surface can be thusrealized.

This embodiment can be freely combined with any of the otherembodiments.

This application is based on Japanese Patent Application Serial No.2011-028914 filed with the Japan Patent Office on Feb. 14, 2011, theentire contents of which are hereby incorporated by reference.

What is claimed is:
 1. A light-emitting module comprising: alight-emitting element; a positive temperature coefficient thermistor;and a substrate between the light-emitting element and the positivetemperature coefficient thermistor, wherein the light-emitting elementincludes a first electrode, a layer including a light-emitting organiccompound over the first electrode and a second electrode over the layerincluding the light-emitting organic compound, wherein the positivetemperature coefficient thermistor includes a third electrode, whereinthe light-emitting element and the positive temperature coefficientthermistor overlap each other, wherein the light-emitting element isconfigured to be supplied with electric power through the positivetemperature coefficient thermistor, wherein the positive temperaturecoefficient thermistor is configured to interrupt or inhibit supply ofthe electric power to the light-emitting element, wherein the substratecomprises an opening, and wherein the first electrode of thelight-emitting element is electrically connected to the third electrodeof the positive temperature coefficient thermistor through the openingof the substrate.
 2. The light-emitting module according to claim 1,wherein an operation temperature of the positive temperature coefficientthermistor is greater than or equal to 100° C. and less than or equal to200° C.
 3. The light-emitting module according to claim 2, wherein thepositive temperature coefficient thermistor comprises a material inwhich electrically conductive filler is dispersed in a polymer positivetemperature coefficient material or a material in which a rare earthelement is added to barium titanate.
 4. The light-emitting moduleaccording to claim 1, wherein the light-emitting element is thermallycoupled with the positive temperature coefficient thermistor through anelectrically conductive material.
 5. The light-emitting module accordingto claim 1, wherein the light-emitting element is located over thepositive temperature coefficient thermistor, and wherein light emittedby the layer including the light-emitting organic compound is extractedthrough the second electrode.
 6. The light-emitting module according toclaim 1, wherein the light-emitting module is incorporated into alighting device.
 7. The light-emitting module according to claim 1,wherein the positive temperature coefficient thermistor is configured tointerrupt or inhibit supply of the electric power to the light-emittingelement when the positive temperature coefficient thermistor detects atemperature higher than an operation temperature of the positivetemperature coefficient thermistor.
 8. The light-emitting moduleaccording to claim 1, further comprising an insulating layer between thelight-emitting element and the positive temperature coefficientthermistor.
 9. A light-emitting module comprising: a light-emittingelement; a first positive temperature coefficient thermistor; a secondpositive temperature coefficient thermistor electrically directlyconnected in series to the first positive temperature coefficientthermistor; and a substrate between the light-emitting element and eachof the first positive temperature coefficient thermistor and the secondpositive temperature coefficient thermistor, wherein the light-emittingelement includes a first electrode, a layer including a light-emittingorganic compound over the first electrode and a second electrode overthe layer including the light-emitting organic compound, wherein each ofthe first positive temperature coefficient thermistor and the secondpositive temperature coefficient thermistor includes a third electrode,wherein the light-emitting element overlaps with each of the firstpositive temperature coefficient thermistor and the second positivetemperature coefficient thermistor, wherein the light-emitting elementis configured to be supplied with electric power through the firstpositive temperature coefficient thermistor and the second positivetemperature coefficient thermistor, wherein the first positivetemperature coefficient thermistor and the second positive temperaturecoefficient thermistor are configured to interrupt or inhibit supply ofthe electric power to the light-emitting element, wherein the substratecomprises an opening, and wherein the first electrode of thelight-emitting element is electrically connected to the third electrodeof each of the first positive temperature coefficient thermistor and thesecond positive temperature coefficient thermistor through the openingof the substrate.
 10. The light-emitting module according to claim 9,wherein an operation temperature of each of the first positivetemperature coefficient thermistor and the second positive temperaturecoefficient thermistor is greater than or equal to 100° C. and less thanor equal to 200° C.
 11. The light-emitting module according to claim 9,wherein the first positive temperature coefficient thermistor and thesecond positive temperature coefficient thermistor comprise a materialin which electrically conductive filler is dispersed in a polymerpositive temperature coefficient material or a material in which a rareearth element is added to barium titanate.
 12. The light-emitting moduleaccording to claim 9, wherein the light-emitting element is thermallycoupled with the first positive temperature coefficient thermistor andthe second positive temperature coefficient thermistor through anelectrically conductive material.
 13. The light-emitting moduleaccording to claim 9, wherein the light-emitting element is located overthe first positive temperature coefficient thermistor and the secondpositive temperature coefficient thermistor, and wherein light emittedby the layer including the light-emitting organic compound is extractedthrough the second electrode.
 14. The light-emitting module according toclaim 9, wherein the light-emitting module is incorporated into alighting device.
 15. The light-emitting module according to claim 9,wherein the first positive temperature coefficient thermistor and thesecond positive temperature coefficient thermistor are configured tointerrupt or inhibit supply of the electric power to the light-emittingelement when at least one of the first positive temperature coefficientthermistor and the second positive temperature coefficient thermistordetects a temperature higher than an operation temperature of the one ofthe first positive temperature coefficient thermistor and the secondpositive temperature coefficient thermistor.
 16. The light-emittingmodule according to claim 9, further comprising an insulating layer,wherein the insulating layer is between the light-emitting element andeach of the first positive temperature coefficient thermistor and thesecond positive temperature coefficient thermistor.